There exist different methods of manufacturing shaped parts from powders using Hot Isostatic Pressing technique. The main feature of these techniques is that free shaping (volumetric shrinkage) of a piece is performed by isostatic gas pressure at high temperatures and therefore there is no any rigid tool conventional for traditional processes of hot metal forming. All these methods use metallic cans or capsules as a plastically deformed tool to give initial shape to powder and to transfer external HIP pressure on it.
Usually capsules with constant wall thickness of 2-3 mm are used for HIP. Along with advantages of this method such as the possibility of manufacturing large-size parts with isotropic structure of material and 100% density it has some serious disadvantages while complex shape parts are considered:
during HIP in capsules with constant wall thickness substantial distortions caused by radial shrinkage occur and lead to poor dimensional precision of the powder parts and low material yield; PA1 irregularity of powder tap density in different sections and channels of the capsule and local deviations in capsule and powder material properties lead to difficulties in controlling the shrinkage and final shape of complex shape parts such as turbine and compressor disks with blades and as a result-cause shape distortions after HIP; PA1 if powders with tap density less than 65-70% are used for HIP, it leads to strong distortions during shrinkage and makes it impossible to manufacture shaped parts using the above method;
During conventional HIP of powders with 65-70% initial density in capsules with constant wall thickness the values of radial and axial shrinkage constitute 12-13% and 14-16% correspondingly.
For large size parts such as turbine disks of 500-600 mm (20-24") diameter these values of radial shrinkage can reach 60-70 mm (2.5-3"). Such large radial deformations inevitably lead to geometrical distortions of parts during HIP. Therefore it is necessary to reduce the absolute values of radial deformations during HIP. Besides, while manufacturing parts by conventional HIP method in capsules with constant wall thickness only powders with high tap density (more than 55-60%) can be used, otherwise initial internal pressure inside the capsule is so low that the capsule looses its shape under high external pressure during radial shrinkage. This does not enable to manufacture by HIP parts with desired geometry from many perspective powder materials such as powders of refractory alloys with initial density less than 30%. In order to have active control of the shrinkage process and of the final geometry the following manufacturing method based on shrinkage regulation by a new design of capsules with variable wall thickness is proposed.